A voltage regulator converts an input voltage VIN from an input power supply to produce a regulated output voltage VOUT. For conserving power and extending the life of the input power supply, it is essential to maintain low quiescent current of the voltage regulator. Providing a low level of quiescent current is especially important for battery powered applications.
To reduce quiescent current and extend battery life, a voltage regulator may be placed into a sleep mode during which power supplied to internal circuits is cut or reduced. A conventional voltage regulator monitors its regulated output voltage to determine when it would enter and exit sleep mode. If its output voltage is higher than a pre-programmed regulation point, it would go into a sleep mode. If the output voltage is reduces below the regulation point, the voltage regulator would wake up to recharge the output.
However, this conventional scheme of a sleep mode control would not work in a dropout mode when the input voltage VIN approaches the output voltage VOUT, and a difference between VIN and VOUT becomes less than a dropout voltage, which is the smallest possible difference between VIN and VOUT that allows the regulator to remain inside the regulator's intended operating range. Dropout voltage may vary depending on the load on the regulator, usually increasing at higher load, due to the internal resistance of the regulator's pass transistor and circuitry. Dropout voltage may also vary depending on temperature.
When a difference between VIN and VOUT becomes less than the dropout voltage, the output voltage VOUT starts to drop out of regulation. At that point, the conventional regulator would stay awake all the time because its VOUT is now always below its programmed regulation point.
However, for battery powered applications, it would be desirable to create a new voltage regulator sleep control scheme that would allow a voltage regulator to go into a sleep mode even when the output voltage VOUT has fallen below its programmed regulation point, so as to reduce quiescent current and maximize operational lifetime.